Unit 4

Question 1

What does resonance mean for atomic absorption

Answer 1

In order to excite the energy must be EXACTLY enough to excite (not above nor below)

Question 2

Sodium Vapour Lamps

Answer 2

As the lamp heats up, sodium is vaporized and excited in the plasma producing light

Question 3

What is the energetically favoured excitation

Answer 3

HOMO to LUMO

Question 4

What are the axes in absorption spectra

Answer 4

Y= absorption X=Wavelength

Question 5

Why does molecular absorption have wider bandwidth

Answer 5

Its excitation is possible at vibrational and rotational wavelengths as well as electronic

Question 6

What happens as wavelength increases

Answer 6

As wavelength increases ΔE decreases

Question 7

What does auxochrome do

Answer 7

Functional group that alters light absorption

Question 8

What is the triplet state

Answer 8

When the spin switches when excited

Question 9

Fluorescence vs Phosphorescence

Answer 9

Phosphorescence is when the spin is switched (triplet state) thus its relaxation takes longer (needs to switch back) and light is emitted longer

Question 10

What is a chromophore

Answer 10

The location on a molecule responsible for electronic transition

Question 11

The Effect of Conjugation on Chromophores

Answer 11

shifts the absorption maximum to longer wavelengths

Question 12

What is the consequence of light being absorbed at a higher wavelength

Answer 12

ΔE (the HOMO-LUMO gap) will decrease

Question 14

Beer-Lambert Law

Answer 14

A=εbC

Question 15

What is transmitted light

Answer 15

the amount of light that passes through a sample

Question 16

How to calculate absorbance from transmitted light

Answer 16

A=−log(T) (T as a decimal)

Question 17

What is the slope in Beers Lambert plot

Answer 17

εb

Question 18

What would a larger slope on Beers Lambert plot indicate

Answer 18

Higher sensitivity

Question 19

Why do we measure at max wavelength

Answer 19

Higher sensitivity

Question 20

What does ε mean

Answer 20

Measure of how strongly a molecule absorbs light

Question 21

Instrumentation order for spectrophotometer (single beam)

Answer 21

Light, Monochromator, Sample, Detector, Computer

Question 22

When should Tungsten halogen lamp be used

Answer 22

For visible light

Question 23

When should Deuterium lamp be used

Answer 23

For UV light

Question 24

What does Diffraction Grating Monochromators do

Answer 24

Select a particular wavelength of light by utilizing the fact that different wavelengths of diffracted light experience constructive interference at different angles

Question 25

What do each of terms in a-b=mλ= d(sini +sinr) mean

Answer 25

m=order of diffraction r= angle of diffraction i=angle of incidence d=groove spacing

Question 26

Czerny-Turner Grating Monochromatic Configuration

Answer 26

slit, mirror, grating, mirror, slit

Question 27

What m indicates constructive interference

Answer 27

a whole number

Question 28

What is the benefit and consequence of a more narrow entrance/exit slit

Answer 28

less sensitive (S/N decreases) but better resolution

Question 29

What is the result of higher groove density

Answer 29

More dispersion

Question 30

Double monochromator configuration

Answer 30

entrance slit- grating -slit- grating -exit slit

Question 31

What cuvette do you use for UV

Answer 31

Quartz

Question 32

Photoelectric effect

Answer 32

Light shone on metal will eject electrons

Question 33

How does Deuterium Light Work

Answer 33

It excites deuterium and light is released as it relaxes

Question 34

Benefits of vapour phase

Answer 34

More vibrational and rotational freedom thus finer structure is absorbed